|
|
PDF LT1946EMS8 Data sheet ( Hoja de datos )
| Número de pieza | LT1946EMS8 | |
| Descripción | 1.2MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT1946EMS8 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
|
No Preview Available !
LT1946
1.2MHz Boost
DC/DC Converter with
1.5A Switch and Soft-Start
FEATURES
s 1.5A, 36V Internal Switch
s 1.2MHz Switching Frequency
s Integrated Soft-Start Function
s Output Voltage Up to 34V
s Low VCESAT Switch: 300mV at 1.5A (Typ)
s 8V at 430mA from a 3.3V Input
s Small 8-Lead MSOP Package
U
APPLICATIO S
s TFT-LCD Bias Supplies
s GPS Receivers
s DSL Modems
s Local Power Supplies
DESCRIPTIO
The LT®1946 is a fixed frequency step-up DC/DC converter
containing an internal 1.5A, 36V switch. Capable of gener-
ating 8V at 430mA from a 3.3V input, the LT1946 is ideal
for large TFT-LCD panel power supplies. The LT1946
switches at 1.2MHz, allowing the use of tiny, low profile
inductors and low value ceramic capacitors. Loop com-
pensation can be either internal or external, giving the user
flexibility in setting loop compensation and allowing opti-
mized transient response with low ESR ceramic output
capacitors. Soft-start is controlled with an external capaci-
tor, which determines the input current ramp rate during
start-up.
The 8-lead MSOP package and high switching frequency
ensure a low profile overall solution less than 1.2mm high.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
L1
4.7µH
D1
3.3V
65
3 VIN
OFF ON
SHDN
SW
C1
2.2µF
RC
49.9k
CC
470pF
LT1946
12
VC FB
SS COMP GND
CSS 8 7 4
100nF
C1: 2.2µF, X5R OR X7R, 6.3V
C2: 2 × 10µF, X5R OR X7R, 10V
D1: MICROSEMI UPS120 OR EQUIVALENT
L1: TDK RLF5018T-4R7M1R4
R1
28.7k
R2
5.23k
VOUT
8V
430mA
C2
20µF
1946 F01
Figure 1. 3.3V to 8V, 430mA Step-Up DC/DC Converter
Efficiency
90
85
80
75
70
65
60
55
50
0 100 200 300 400 500
LOAD CURRENT (mA)
1946 F01b
sn1946 1946fs
1
1 page  
U
OPERATIO
The LT1946 uses a constant frequency, current mode
control scheme to provide excellent line and load regula-
tion. Please refer to Figure 2 for the following description
of the part’s operation. At the start of the oscillator cycle,
the SR latch is set, turning on the power switch Q1. The
switch current flows through the internal current sense
resistor generating a voltage. This voltage is added to a
stabilizing ramp and the resulting sum is fed into the
positive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative input of A2, the SR
latch is reset, turning off the power switch. The level at the
negative input of A2 (VC pin) is set by the error amplifier
(A1) and is simply an amplified version of the difference
between the feedback voltage and the reference voltage of
1.250V. In this manner, the error amplifier sets the correct
peak current level to keep the output in regulation.
Two functions are provided to enable a very clean start-up
for the LT1946. Frequency foldback is used to reduce the
oscillator frequency by a factor of 3 when the FB pin is
LT1946
below a nominal value of 0.5V. This is accomplished via
comparator A3. This feature reduces the minimum duty
cycle that the part can achieve thus allowing better control
of the switch current during start-up. When the FB pin
voltage exceeds 0.5V, the oscillator returns to the normal
frequency of 1.2MHz. A soft-start function is also provided
by the LT1946. When the part is brought out of shutdown,
4µA of current is sourced out of the SS pin. By connecting
an external capacitor to the SS pin, the rate of voltage rise
on the pin can be set. Typical values for the soft-start
capacitor range from 10nF to 200nF. The SS pin directly
limits the rate of rise on the VC pin, which in turn limits the
peak switch current. Current limit is not shown in Figure 2.
The switch current is constantly monitored and not al-
lowed to exceed the nominal value of 2.1A. If the switch
current reaches 2.1A, the SR latch is reset regardless of
the output of comparator A2. This current limit helps
protect the power switch as well as the external compo-
nents connected to the LT1946.
APPLICATIO S I FOR ATIO
Inductor Selection
Several inductors that work well with the LT1946 are listed
in Table 1. This table is not exclusive; there are many other
manufacturers and inductors that can be used. Consult
each manufacturer for more detailed information and for
their entire selection of related parts, as many different
sizes and shapes are available. Ferrite core inductors
should be used to obtain the best efficiency, as core losses
at 1.2MHz are much lower for ferrite cores than for the
cheaper powdered-iron ones. Choose an inductor that can
handle at least 1.5A without saturating, and ensure that the
inductor has a low DCR (copper wire resistance) to mini-
mize I2R power losses. A 4.7µH to 10µH inductor will be
the best choice for most LT1946 designs. Note that in
some applications, the current handling requirements of
the inductor can be lower, such as in the SEPIC topology
where each inductor only carries one-half of the total
switch current.
The inductors shown in Table 1 were chosen for small size.
For better efficiency, use similar valued inductors with a
larger volume.
Table 1. Recommended Inductors
PART
MAX
L DCR
(µH) (mΩ)
SIZE
L×W×H
(mm)
CDRH5D18-4R1
CDRH5D18-5R4
CDRH5D28-5R3
CDRH5D28-6R2
CDRH5D28-8R2
4.1
5.4
5.3
6.2
8.2
57 5.7 × 5.7 × 2
76
38 5.7 × 5.7 × 3
45
53
ELL6SH-4R7M 4.7 50 6.4 × 6 × 3
ELL6SH-5R6M 5.6 59
ELL6SH-6R8M 6.8 62
RLF5018T-
4R7M1R4
4.7 45 5.6 × 5.2 × 1.8
VENDOR
Sumida
(847) 956-0666
www.sumida.com
Panasonic
(408) 945-5660
www.panasonic.com
TDK
(847) 803-6100
www.tdk.com
sn1946 1946fs
5
5 Page 
PACKAGE DESCRIPTIO
MS8 Package
8-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1660)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
3.2 – 3.45
(.126 – .136)
0.42 ± 0.04
(.0165 ± .0015)
TYP
0.65
(.0256)
BSC
RECOMMENDED SOLDER PAD LAYOUT
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
8 7 65
0.52
(.206)
REF
0.254
(.010)
DETAIL “A”
0° – 6° TYP
4.88 ± 0.1
(.192 ± .004)
3.00 ± 0.102
(.118 ± .004)
NOTE 4
GAUGE PLANE
0.53 ± 0.015
(.021 ± .006)
DETAIL “A”
1 234
1.10
(.043)
MAX
0.18
(.077)
SEATING
PLANE 0.22 – 0.38
(.009 – .015)
0.65
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
(.0256)
BCS
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.86
(.034)
REF
0.13 ± 0.05
(.005 ± .002)
MSOP (MS8) 1001
LT1946
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
sn1946 1946fs
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LT1946EMS8.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT1946EMS8 | 1.2MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |